Few investigations dealing with detoxification or activation of carcinogens by the microsomal mixed-function oxidase (MFO) system have examined the amount and localization of the individual enzymes which comprise the MFO system. With immunological methods, we propose to localize and quantitate the MFO components in rat liver. Hepatoma tissue will be compared with intact tissue both with respect to intrahepatic distribution of these components and the hydroxylating activity of the microsomal fraction. Livers of untreated rats will be compared with those challenged in vivo with water and lipid-soluble carcingens as well as substances which either augment or inhibit the carcinogenic effect.